1. Field of the Invention
The present invention relates to the fields of oil chemistry, gas chemistry, coal chemistry and technique for preparing catalysts used in reactions of hydrogenation of carbon monoxide, for example, for producing hydrocarbons from CO and H2 via Fisher-Tropsch method (synthesis), ultra-liquid C5+ products, such as synthetic oil and components of motor fuels, or synthesis products for subsequent processing in petrochemical and gasochemical processes. In particular, the invention relates to a method for producing C5+ hydrocarbons over a cobalt catalyst in “gas to liquid” processes (XTL) where a syngas source can be any of organic (carbon-containing) substances such as gas and liquid hydrocarbons or mixtures thereof, gas hydrates, coal, shales, biomass.
2. Description of the Related Art
Synthesis of hydrocarbons from COH2 proceeds in the presence of catalysts based on metals of group VIII of the Mendeleev's periodic table. The catalyst composition defines a composition of the obtained products. Cobalt catalysts are considered as selective catalysts for synthesis of paraffins. The presence of cobalt applied on oxide supports generally results in formation of linear paraffins. Cobalt catalysts on zeolites or mixed oxides are used to obtain a product with high content of branched paraffins. In this case, hydrocarbons of gasoline fraction (C5-C10) with isomer content up to 80% are generally obtained. However, high content of branched hydrocarbons in diesel fraction (C11-C18) is equally important because it decreases the cloud point temperature (freezing temperature) and viscosity of the resulting diesel fuel. Pour point temperature and viscosity are also important for pipeline transportation of synthetic oil together with mineral oil.
It is known that hydrocarbons can undergo various transformations in the presence of solid acids among which are mixed oxides and zeolites (Zeolite chemistry and catalysis, V. 2, Edited by J. Rabo, Moscow, 1980, p. 422; V. U. S. Rao, R. J. Gormley. Catal. Today. 1990. V. 6. P. 207; H. Van Bekkum, E. M. Flanigen, J. C. Jansen Stud. Surf. Sci. Catal. 1991. V. 58. P. 455). Application of metal salts on a solid acid such as zeolite leads to formation of catalysts functioning as metal and acid contacts. Olefins formed from CO and H2 on metallic sites or their intermediates can undergo secondary transformation, such as isomerization and/or hydroisomerization, on acid sites to form aromatic or branched aliphatic hydrocarbons, and alkanes can undergo hydrocracking to form shorter hydrocarbon chains. Generally, the isomerization/hydroisomerization proceeds at lower temperature as compared with hydrocracking. The ratio of synthesis products will probably be defined by relative rates of reactions on the acid and metal sites. In this case, since increase in the syngas velocity accelerates mass exchange, olefin residence time in pores filled with liquid decreases, and therefore the probability of the olefin secondary transformation on the zeolite component of the catalyst decreases.
Known in the art is a Fisher-Tropsch synthesis catalyst to reduce the yield of methane by-product and increase the yield of C5+ olefins, wherein a cobalt catalyst for Fisher-Tropsch synthesis is applied on zeolite molecular sieves (patent JP 2083038A, 1990). Preparation of this catalyst comprises steaming the molecular sieve LZ-2/0, in which the initial SiO2/Al2O3 ratio is 8.0, to obtain the TC-123 support, and filling pores of said molecular sieves with ethylene glycol solution, water, alcohol and the like comprising a Co- and Mn-containing promoter. In the presence of the Fisher-Tropsch synthesis catalyst prepared by that way and containing 8.2% of Co and 1.6% of Mn/TC-123, the selectivity of the methane formation from CO and H2 at their ratio of 1:1 (feed velocity is 300 hr−1 at 240° C.) can decrease to 3.3% while selectivity of C5+ hydrocarbons formation can increase to 89%. A drawback of this catalyst is its low activity, since the conversion of CO in the presence of this catalyst was less than 48% even in a reactor of 3 mm in diameter.
Also known in the art is a Fischer-Tropsch synthesis catalyst comprising cobalt, scandium and a suitable support (patent application WO/1993/005000 A1). The application also describes a process for producing hydrocarbons from a syngas (CO+H2) in the presence of this catalyst. The support may be silica gel, alumina, silica-alumina and kieselguhr, if the required product is wax or middle distillates. Alternatively, the support may be a molecular sieve or zeolite, if gasoline or middle distillate and gasoline are to be produced. A drawback of this catalyst is low C2+ hydrocarbons productivity, since the output was no more than 213 mg C2+/g/h at feed velocity of the mixture H2 and CO (2:1) of 1000 hr−1, 240° C. and 2 MPa.
Known in the art is a method of conversion of syngas comprising contacting the syngas with a hybrid bimetallic Fischer-Tropsch catalyst obtained by impregnation of ZSM-12 zeolite granules with a non-aqueous solution of cobalt and ruthenium salts and activated by a reduction-oxidation-reduction procedure (patent application WO/2011/062773 A2). The method provides decreased methane yield and increased yield of solid wax-free liquid hydrocarbons. Drawbacks of this catalyst are low activity (conversion of CO is 24-42%) and productivity (0.122 g CH2/gcat/h).
Also known in the art is a method for producing gasoline hydrocarbon fractions from a syngas of H2k, CO and CO2 by contacting the gas mixture with a catalyst in at least two successive reaction zones at the pressure of 40-100 atm. In the first reaction zone, the gas mixture comes in contact with a bifunctional catalyst comprising zeolite of ZSM-5 or ZSM-11 structure and metal-oxide component composed of oxides of Zn, Cr H W at the temperature of 340-420° C. In the second reaction zone, the gas mixture comes in contact with a monofunctional catalyst comprising zeolite of ZSM-5 or ZSM-11 structure at the temperature of 320-460° C. The gas flow coming out of the reactor is recycled. This method characterized in that the zeolite of the monofunctional catalyst contains iron in the amount of 0.3-1% by weight (patent RU 2339603 C1, 2008). The use of this method enables reducing the regeneration temperature and regeneration time of the monofunctional catalyst. Disadvantages of this process are high synthesis temperature and pressure resulting in high energy consumption, and complicated process flow scheme including at least two reactors and a complicated pipeline system.
Known in the art is a method for preparing a catalyst for synthesis of C5-C10 aliphatic hydrocarbons from carbon monoxide and hydrogen, comprising two-stage impregnating Y or ZSM zeolite with a solution of cobalt nitrate with intermediate calcination in an air stream at the temperature of 350-450° C. and drying to prepare the catalyst having improved activity and selectivity with respect to isoparaffin hydrocarbons (patent RU 2297879 C1, 2007 or patent application WO/2007/121224 A2). In this method, the maximum yield of C5+ hydrocarbons is 122 g/m3, 70% of which is C5-C10 gasoline fraction containing up to 80% isoparaffins. A disadvantage of this method for preparing the catalyst is lack of the stage of calcination after the second impregnation with a water solution of cobalt nitrate, that results in that cobalt nitrate decomposition with nitrogen oxides formation already proceeds in the synthesis reactor, that requires increased attention to the quality of the used materials. A drawback of this catalyst is low activity as the conversion of CO is no more than 54% that requires additional costs for gas recycling.
Known in the art is a composite catalyst comprising a water-gas shift catalyst coated with a thin film of zeolitic material on which, in turn, a Fischer-Tropsch catalyst is deposited (patent application WO/1992/019574 A1). Fischer-Tropsch synthesis by-products, namely a short chain of hydrocarbons and steam, pass through zeolite pores to the water-gas shift catalyst, and carbon monoxide and hydrogen formed over this catalyst diffuse back to the Fischer-Tropsch catalyst on the outer surface of the zeolite and react there to produce hydrocarbon oligomers. The Fischer-Tropsch reaction produces water, therefore the catalyst shall be stable in the presence of steam. The catalyst comprises supports such as silicon oxide, alumina, zirconium oxide, thorium oxide or mixtures thereof coated with a layer of zeolite of 2 to 10 nm in thickness. USY zeolite, silica-rich mordenite, offretite, zeolite omega, ZSM-5, silicalite, X and Y zeolites are used to prepare the catalyst. The composite catalyst also comprises promoters selected from the group consisting of Re, Ru, Pd, Pt, ThO2, ZnO2, Al2O3, MgO and MnO. Moreover, the catalyst may comprise Li, Na, K, Ca, Mg and Fe, Cu or Zn as a component of the water-gas shift catalyst and cobalt as an active metal for Fischer-Tropsch synthesis. Drawbacks of the catalyst are that the catalyst preparation process is complicated and the catalyst cannot be used in a granular bed because the catalyst is in the form of microspheres appropriate for use in slurry reactors.
Known in the art are processes for the single-stage producing of synthetic hydrocarbons enriched in gasoline fraction with high-octane components (aromatic hydrocarbons, naphthenes, olefinic and branched hydrocarbons) as well as catalysts for these processes. The catalysts are a physical mixture of a Fischer-Tropsch catalyst with a hydroisomerization and/or hydrocracking catalysts (patent applications JP 2011125802 A, 2011; US 20110160315 A1, 2011; U.S. Pat. Nos. 7,300,959 B2, 2007; 7,157,501 B2, 2007; 7,973,086 B1, 2011). Disadvantages of these processes are high yield of unsaturated compounds, in particular aromatic hydrocarbons, the presence of which in automobile fuel is outlawed in many countries, high cloud point temperature (2-10° C.) of produced hydrocarbons and low catalyst activity.
Also known in the art is a process for decreasing pour point temperature of hydrocarbons products produced by Fischer-Tropsch synthesis and a catalyst for this process. The catalyst is a mixture of TON structure type zeolites (Theta-1, ZSM-22, ISI-1, NU-10 and KZ-2), at least one ZBM-30 zeolite, at least one inorganic porous matrix, and at least one hydrogenating/dehydrogenating element from the VIB group or group VIII of the periodic table (patent RU 2346977 C2, 2006). The result is that the pour point temperature decreases from 42° C. to minus 24° C. A disadvantage of this process is the need for additional stage in the process flow for producing hydrocarbons from CO and H2.
The process for producing hydrocarbons from CO and H2 (Fischer-Tropsch synthesis) is characterized by exothermicity and sensitivity to the reaction temperature. The increase of the synthesis temperature results in the increase of overall catalyst activity but the selectivity for the target products significantly decreases due to significant increase of the yield of synthesis by-products, namely methane and carbon dioxide. One of alternative solutions of the above-mentioned problems when carrying out the process in a stationary (fixed) bed of the catalyst is increasing thermal conductivity of the granulated catalyst. For that purpose, heat-conductive materials can be used when preparing the Fischer-Tropsch synthesis catalyst. Known in the art is using heat-conductive materials as exothermic processes catalysts supports on which an active component is deposited. Patent EP 1020222 B2, 2004 discloses the use of cylindrical copper granules coated with Al, Zn or Ni as a catalyst for an exothermic process of oxychlorination of ethylene to 1,2-dichloroethane. This catalyst has thermal conductivity of 0.4 W/cm·K.
Known in the art is a method for preparing a catalyst for exothermic processes, consisting in the deposition of several layers of metal alloys on a support of iron, steel, titanium, nickel or copper preheated in an argon stream (patent application WO 200176737 A1, 2001). Disadvantages of these processes are their complexity and high energy consumption and labor input.
Known in the art is a cobalt-based catalyst for synthesis of aliphatic hydrocarbons from CO and H2 (patent RU 2256501 C1, 2005), comprising metal aluminum powder as a support. Additionally, the catalyst may comprise a promoter selected from the group of metal oxides (ZrO2, La2O3, K2O) or metals (Re, Ru, Pd, Pt). The catalyst comprises 10-50 wt. % of Co, 0.5-3 wt. % of the promoter, 50-90 wt % of Al. The catalyst is prepared by impregnation of the aluminum powder with a water solution of cobalt nitrate and by further drying on a water bath and calcination in an air stream at 450° C. during 1 hour. A treatment with hydrogen is carried out at the temperature of 400-600° C. and H2 feed velocity of 100-3000 -1 for 1-5 hours. The synthesis is carried out at the atmospheric pressure and temperature of 160-230° C. from the mixture comprising 66-68 mole % of H2 and 32-34 mole % of CO. Drawbacks of this catalyst are insufficient selectivity and productivity for the target products.
Known in the art is a granulated Fischer-Tropsch synthesis catalyst based on a metal of group VIII of the Mendeleev's periodic table and metal aluminum, as well as a method for preparing the catalyst (patent RU 2326732 C1, 2006). The active metal (5-40% of the catalyst weight) is applied on a support by impregnation. The support is prepared by extrusion from a paste comprising an oxide component (aluminum oxide and/or silicon oxide and/or titanium oxide and/or zirconium oxide), 1-25% of metal aluminum (heat-conducting component) in the form of flakes and 5-15% of SB-1 boehmite as a binding agent. The method for preparing the catalyst comprises preparing the support comprising the oxide component, a metal aluminum powder, diethyl ether, the binding agent, water, a plasticizer and a pore-forming agent by extrusion, drying and calcination, and following sequential stages of impregnation with a solution of the active metal salt. The support may comprise 0.1-5% of promoter (zirconium or metals of groups VII-VIII of the Mendeleev's periodic table and/or their oxides) introduced by impregnation of the support with a solution of the corresponding salts. Before the synthesis, the catalyst is activated in a hydrogen stream (space velocity is 100-5000 h−1) at the temperature of 300-600° C. for 0.5-5 hours. The synthesis of hydrocarbons from CO and H2 is carried out in a tubular fixed bed catalytic reactor at the pressure of 0.1-4 MPa and the temperature of 150-300° C. Molar ratio CO/H2 in the synthesis gas is 1/1 to 3. A drawback of this catalyst is that the active component is applied both on the oxide support and heat-conducting component powder, that requires introduction of the active metal in the amount exceeding the amount required to ensure the claimed activity and selectivity.
A metal phase prevailing in Raney catalysts provides such advantage as high heat conductivity. It is particularly important for efficient heat removal from the reaction zone. The overheating of the deposited catalyst during the synthesis of hydrocarbons from CO and H2 results in the coarsening of cobalt crystallites and decreasing activity and selectivity of this system. Therefore, researchers have repeatedly attempted to create a highly efficient Fischer-Tropsch synthesis catalyst on the base of Raney cobalt. In this regard, improvement of known and development of new methods for preparing initial alloys for skeletal catalysts and conditions of leaching and passivation thereof have allowed resuming researches in this field. Known in the art are catalysts of disperse active metal for using in hydrogenation reactions, which catalysts are different in methods of passivation and activation (U.S. Pat. Nos. 6,531,518, 2003, and 6,706,661, 2004). Drawbacks of these catalysts are low specific activity and low specific productivity. Moreover, these catalysts cannot be used in a granulated fixed bed.
Raney catalysts were tested in the synthesis of hydrocarbons from CO and H2 substantially immediately after discovery of them at the initial stage of the Fischer-Tropsch synthesis development in 1934 (Fischer, F., and Meyer, K. Suitability of Alloy Skeletons as Catalysts for Benzine Synthesis. Brennstoff-Chem., vol. 15, 1934, pp. 84-93, 107-110; Ber. Deut. Chem. Gesell., vol. 67B, 1934, pp. 253-261; Ges. Abhandl. Kenntnis Kohle, vol. 12, 1937, pp. 356-382). It has been determined that these catalysts exhibit activity in the synthesis of hydrocarbons from CO and H2. The Ni—Co—Si alloy (1/2:1/2:1) was the most active. However, the activity of the Raney catalysts was lower than activity of Fe-based catalysts used in the industry at that time. Moreover, the Raney catalysts was characterized by several drawbacks such as high content of an active component, low specific activity (calculated per unit of metal weight), high specific weight, low productivity and pyrophorosity that complicated storing of the catalyst.
At the end of the 60's of the twentieth century, Russian scientists made an attempt to return to the study of skeletal catalysts for the synthesis of hydrocarbons from CO and H2 (Eidus Ya. T. //XTT. 1971, No. 3, pages 654-656). However, the comparison of the results obtained for a skeletal sample on the base of Co—Ni—Al alloy and deposited Co—Ni catalyst promoted by oxides of Al, Mn and Th showed that the deposited catalyst is more preferable.
Known in the art are single attempts to introduce Raney cobalt in the form of an alloy with aluminum in a granulated catalyst, but for using in hydrogenation processes (U.S. Pat. No. 5,536,694, 1996). A method disclosed in this patent comprises preparing a power mixture consisting of at least one alloy and at least one binder, wetting agent and additive consisting of a mixture of a shaping aid, a lubricant, a plasticizer and a pore-forming agent. Raney metal is also used as a binder, but it differs from Raney metal included in the alloy. The alloy consists of at least one Raney metal, a leachable component (Al, Zn, Si or mixtures thereof) and a promoter (Cr, Fe, Co, Ta, Ti or mixtures thereof). The above-mentioned mixture is shaped, dried at 80-120° C. and calcined at 500-700° C. The particle size of the alloy should be 10-500 and the particle size of the binder should be less than the particle size of the alloy. The prepared catalyst consists of more than 99% of the alloy and the binder. The obtained granules are leached with 20% NaOH at 80° C. to activate only an outer layer 0.05-1 mm in thickness. Disadvantages of the method are high labor intensity and high prime cost that complicate commercial use of the method.
Also known in the art is a process for catalytic hydrogenation of CO in several successive three-phase reactors to form a mixture of hydrocarbons (U.S. Pat. No. 6,642,281 B1, 2003), wherein a catalyst at least in the first reactor is a fine-dispersed active metal, namely Raney cobalt. Raney cobalt is prepared by fusion of cobalt with aluminum, titanium, silicon or zinc, crushing the obtained alloy to a powder and then removing aluminum, titanium, silicon or zinc.
Also known in the art is a granulated catalyst for hydrogenation processes in a fixed-bed catalytic reactor and a method of preparing the catalyst (U.S. Pat. No. 4,826,799 A1, 1989). The catalyst comprises Raney metal in the amount of 15-50 parts by weight, high-molecular polymer (for example, polyethylene) in the amount of 1-30 parts by weight, α-alumina in the amount of 1-42 parts by weight and homogeneous. Mineral oil is used as a plasticizer in the amount of 0-40 parts by weight. This mixture is shaped by extrusion or fusion and calcined at the temperature of 850-1200° C. to remove the polymer and the plasticizer. The mixture is then treated with a solution of sodium hydroxide to remove aluminum from the alloy. The catalyst may comprise promoters introduced in the initial Raney alloy and selected from the group consisting of Cr, Mo, Ru, Rh, Pd, Os, Ir, and Pt. The catalyst has the BET specific surface area of 20-80 m2/g and macropore volume of 0.1-70% of the total pore volume. A disadvantage of this process is need for a high-temperature treatment that requires a special equipment and significantly increases the cost of the catalyst.
Considered the closest prior art to the present invention is a catalyst for synthesis of hydrocarbons from CO and H2, which is a granulated porous composite material comprising three-dimensional heat-conducting structure of metal aluminum and Raney cobalt as well as a binding component (RU 2405625C1, 2010, having WO 2010/147513 A2, 2010 in its family). This known catalyst comprises Raney cobalt as at least one active component in the amount of 1-40% of catalyst weight, metal aluminum in the amount of 25-94% of catalyst weight and a binding component in the amount of 5-30% of catalyst weight. Raney cobalt in the known catalyst is in the form of fine powder, including cobalt carbonyl powder. A method for preparing this catalyst comprises mixing of Raney cobalt powder, metal aluminum powder and binding component powder with liquid phase, preparing granules of the mixture by extrusion of the obtained paste, drying and calcination of the prepared granules. The known catalyst has high tolerance to overheating and provides high productivity for synthesis of C5-C10 hydrocarbons. A drawback of this catalyst and the method for preparing same is that the catalyst structure obtained by this method does not provide adequate mass transfer of molecules of the reagents and products inside the granule while content of isoparaffins in the produced synthetic oil is insufficient.